The invention relates to a method of manufacturing of brushes, in particular, tooth brushes having a body, which is formed by injection molding, with a head portion having a plurality of through-openings and a back side recess extending over all of the openings and with bristle bundles inserted into the openings.
When the tooth brushes are manufactured, conventionally a handle connected with the brush head by the brush neck is also injection molded in an appropriately designed mold, with the head being subsequently provided with bristle bundles. For providing the brush head with bristle bundles, it is known to form during injection molding of the brush head, bristle bundle receiving openings therein in the form of blind holes. The number of openings corresponds to the number of bristle bundles to be received therein.
To secure the bristle bundles in the openings, the separate bristle bundles are removed, by a suitable device, from a stack of bristle bundles, are creased and then are stuffed into the respective openings in the brush head. The creasing is effected in a special anchor formed of a suitable metal. The width of the anchor is slightly greater than the cross-section of a bristle bundle. This results in that the ends of the anchor, which project beyond the bristle bundle are pressed into the head material radially of the head openings. To this end, relatively small slots are formed in the bristle receiving surface of the head, which are almost invisible by a naked eye and which can be made without much difficulty. However, these metal anchors adversely affect recycling properties of tooth brushes. Because of the metal anchor, the brush head cannot be economically processed for further use.
For reusing of the tooth brush material, the brush head with bristles should be separated, and only the material of the tooth brush handle and neck, are suitable for further use. The brush heads with the bristles are thrown away into a waste dump.
U.S. Pat. No. 3,604,043 discloses a method of manufacturing brushes in which bristle bundles are removed from a container and then are welded at their fastening ends which take a particular shape. Finally, the finished bristle bundles are inserted into blind holes, which are formed in the brush head and are enlarged at their inner end. The fastening end of bristle bundles is so deformed that they are reliably held in the brush body. However, this method is relatively expensive, and it is difficult to enlarge a blind hole.
According to another method of manufacturing tooth brushes, bristle bundles, which are cut to a predetermined length, are inserted into respective channels of a metal plate-like carrier, with their fastening ends being subsequently fused to form thickenings thereat. Then the carrier, with the bristle bundles secured thereto, is placed in a special device against already fused bristle receiving surface of a tooth brush having a brush head, neck and handle. The carrier provides that only the thickenings of the fastening ends of the bristle bundles are received within the fused bristle receiving surface.
After the cooling of the fused bristle receiving surface, the bristle bundles are secured to the brush head. A tooth brush produced by the above-described method is completely recycleable. However, the drawback of this method consists in that during insertion of the thickenings of the fastening ends of the bristle bundles into the fused bristle receiving surface, material accumulation around the bristle bundles takes place, which adversely affect the optical impression such a tooth brush produces.
A similar method is disclosed in German patent No. 845,933. However, in the German patent, the carrier for receiving the cut-off bristle bundles is formed as a mold half which, after being equipped with the bristle bundles and the formation of thickenings, is assembled at its fastening end surface, with another mold half to form an injection mold in which the tooth brush handle is formed, simultaneously with the attachment of the bristle bundles to the brush head. With this method, the mold half that produces openings in the brush head is not used during the attachment of the bristle bundles to the brush head and is inverted.
The prior art also discloses a method of manufacturing of a tooth brush from a thermoplastic material according to which, a first part of the brush head having through openings, is formed in a first injection molding step. Then, the bristle bundles are inserted into the through-openings in the formed brush head part in an injection mold, with the active ends being appropriately shaped and the inner ends being fused. Fusing of the inner ends of the bristle bundles insures their attachment to the first brush head part.
Then, a second part of the brush head is formed in a second injection molding step, in which the first part is molded with the second injection-molded part, which covers the inner ends of the bristle bundles. The drawback of this method consists in that the attachment of the bristle bundles to the brush head in the injection mold increases the production cycle time.
The rounding off of the end of the bristle bundles by grinding with this method is practically excluded because it would require insertion of a grinding head into the injection mold, which would adversely affect the quality of the tooth brush. Accordingly, one object of the invention is a method of manufacturing brushes in particular, tooth brushes, and which would result in producing of recycleable brushes and with a shortened cycle time.
Another object of the invention is a method of manufacturing brushes which would permit insertion of both creased bristle bundles and bristle cut-off section.